Air Pollution: Myths And Facts

Air pollution is a pressing issue that affects people worldwide and has various adverse health effects. It refers to the presence of harmful substances in the air, including solid and liquid pollutants such as nitrogen dioxide, sulfur dioxide, particulate matter, and carbon monoxide. One of the most visible forms of outdoor air pollution is photochemical smog, caused by a mixture of pollutants accumulating during radiation inversion. Additionally, indoor air quality is also a concern, with sources of pollution ranging from pathogenic organisms to inadequate ventilation. Understanding which statements about air pollution are true or false is crucial for mitigating its impact on human health and the environment.

Photochemical smog

Nitrogen oxides, such as nitric oxide (NO) and nitrogen dioxide (NO2), are introduced into the atmosphere through the combustion of fossil fuels. When exposed to sunlight, these nitrogen oxides react with other molecules in the air to form smog. Specifically, NO from combustion engines absorbs the ultraviolet energy of sunlight, releasing free atoms of oxygen (O). These oxygen atoms then combine with molecular oxygen (O2) in the air to form ozone (O3) near the Earth's surface.

Ozone at ground level, also known as tropospheric ozone, is a harmful pollutant that can irritate and damage the membranes of the respiratory system and eyes. Even small traces of ozone and other photochemical oxidants, such as nitrogen dioxide (NO2) and peroxyacetyl nitrate (PAN), can have adverse effects on the respiratory tract of humans and animals, as well as damage crops and trees. These oxidants can react with and oxidize certain compounds in the atmosphere or within a person's lungs that are not normally oxidized.

In addition to ozone, photochemical smog contains other harmful pollutants, including nitric acid and organic compounds. These compounds are trapped near the ground by temperature inversion and can have negative impacts on human health and the environment. The radicals in the air also interfere with the natural nitrogen cycle by preventing the destruction of ground-level ozone. Furthermore, photochemical smog can reduce visibility and cause eye irritation due to the presence of aldehydes and other chemical compounds.

Carbon Monoxide

CO pollution occurs primarily from emissions produced by fossil fuel-powered engines, including motor vehicles and non-road engines such as construction equipment and boats. Other sources of CO emissions include industrial processes (such as metal processing and chemical manufacturing), residential wood burning, and natural sources such as forest fires.

Indoor sources of CO include wood stoves, gas stoves, malfunctioning or improperly vented gas appliances (such as water heaters, furnaces, and clothes dryers), space heaters, fireplaces, tobacco smoke, and car exhaust fumes. The highest levels of CO typically occur during the colder months of the year when inversion conditions (when air pollution becomes trapped near the ground beneath a layer of warm air) are more frequent.

Breathing air with a high concentration of CO reduces the amount of oxygen transported in the blood to critical organs like the heart and brain. Exposure to lower levels of CO is most serious for those with heart disease and can cause chest pain, reduced exercise capacity, and other cardiovascular effects. Even healthy individuals can experience negative effects from high levels of CO exposure, including vision problems, reduced ability to work or learn, impaired manual dexterity, and difficulty performing complex tasks.

Under the Clean Air Act, the U.S. Environmental Protection Agency (EPA) sets and reviews standards for CO in outdoor air to ensure it is maintained at a safe level. While the EPA's review of the National Ambient Air Quality Standard for Carbon Monoxide in 2011 did not find evidence of ecological effects, there is substantial evidence that CO adversely affects human health and contributes to climate change. As a result, CO emission reductions are considered a potential strategy to mitigate the effects of global warming.

Radon

Outdoors, radon quickly dilutes to very low concentrations and is generally not a problem. The average outdoor radon level varies from 5 Bq/m3 to 15 Bq/m3. However, radon can enter buildings through cracks in the floors, walls, or foundations, gaps around pipes or cables, small pores in walls, or through drains. Radon levels are usually higher in basements, cellars, and ground-floor living spaces, but considerable concentrations can also be found above the ground floor.

The health risks associated with radon exposure are primarily related to lung cancer. As radon is breathed in, the radioactive particles are deposited on the cells lining the airways, where they can damage DNA and potentially lead to lung cancer. To date, epidemiological studies have not found a connection between consuming drinking water containing radon and an increased risk of stomach cancer.

High radon levels in buildings can be reduced through various corrective actions. These include preventing radon from entering the indoor environment through isolation and indoor air pressure manipulation, as well as improving ventilation rates and thermal retrofitting of existing buildings. Many national building codes now include preventing radon accumulation in newly constructed houses.

Nitrogen Oxides

NOx gases are also produced naturally by lightning, and the oxidation of NOx from lightning can produce nitric acid, which contributes to acid rain. Additionally, human activities such as the use of nitrogen-based fertilisers in agriculture can contribute to NOx emissions. When excess ammonium and nitrate from fertilisers are not utilised by plants, they can be converted by soil microorganisms into NO, which escapes into the air.

The health effects of nitrogen dioxide and other nitrogen oxides are well-documented. They can cause a range of harmful effects on the lungs, including inflammation, and increased likelihood of hospital admissions. Exposure to NO2 has also been linked to the development of asthma in children. However, it is important to note that nationwide efforts to reduce nitrogen dioxide emissions, such as the federal Clean Air Act, have led to improved air quality in many areas, with lower levels of nitrogen dioxide compared to previous decades.

Particulates

Particulate matter (PM) is a term used to describe a mixture of solid particles and liquid droplets found in the air. These particles are often referred to as particle pollution and can be a mixture of many chemical species, including inorganic ions, metallic compounds, elemental carbon, organic compounds, and compounds from the earth's crust.

PM can be categorised into two main types: inhalable coarse particles and fine particles. Coarse particles have diameters between 2.5 and 10 micrometers (PM10), while fine particles are 2.5 micrometers or less in diameter (PM2.5). These fine particles are the main cause of reduced visibility (haze) in some regions of the United States. They are also associated with the greatest proportion of adverse health effects related to air pollution, both in the US and worldwide, according to the World Health Organization's Global Burden of Disease Project.

The sources of particulate matter vary. Some particles, like dust, dirt, soot, or smoke, are large enough to be seen, while others are so small they require an electron microscope for detection. PM2.5 particles are often emitted directly from sources such as construction sites, unpaved roads, fields, smokestacks, or fires. They can also form in the atmosphere through complex reactions of chemicals like sulfur dioxide and nitrogen oxides, which are pollutants emitted from the combustion of gasoline, oil, diesel fuel, or wood.

The health effects of particulate matter have been a growing concern. Short-term exposures to PM10 have been linked to the worsening of respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD). Long-term exposure to PM2.5 has been associated with premature death, especially in individuals with chronic heart or lung diseases. The Environmental Protection Agency has reported that the inhalation of fine particles is causally associated with premature death at concentrations experienced by many Americans daily.

To address these concerns, organisations like the US EPA have implemented regulations and standards to reduce emissions and protect public health. The Air Quality Index (AQI) is a helpful tool that translates air quality data into numbers and colours, enabling people to take appropriate actions to protect their health. Additionally, the EPA's national and regional rules aim to help state and local governments meet the Agency's national air quality standards.

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